1. Field of the Invention
The invention pertains to high voltage generator circuitry for use with electrostatic spray apparatus.
2. The Prior Art
It has been known that operating advantages might be attained through the use of electrostatic spray pistols wherein the high voltage generation circuitry, typically a 10-12 stage diode-capacitor voltage multiplier circuit, is located within the body of the hand-held unit.
U.S. Pat. No. 3,599,038 to Skidmore shows a hand-held piston with a low frequency diode-capacitor voltage multiplier circuit mounted within the pistol.
U.S. Pat. No. 3,731,145 to Senay and U.S. Pat. No. 3,608,823 to Buschor teach the use of a high frequency pulsating source to drive the gun-mounted diode-capacitor multiplier circuitry. Buschor and Senay allege that, at high frequencies, substantial reductions may be made in the capacitance value, hence physical size and weight, of each capacitor in the diode-capacitor multiplier circuit.
Another advantage to high frequency operation is that the amount of energy stored in the capacitors of the diode-capacitor multiplier circuit can be substantially reduced. Senay in particular teaches the importance of storing minimal amounts of energy in the capacitors of the diode-capacitor multiplier circuit so as to minimize sparking and ignition of flammable paint solvents.
Experience has indicated, however, that the minimal energy storage configuration of Senay does have disadvantages. As capacitance size is decreased, at a given input frequency, toward a minimum capacitor size capable of generating the necessary high voltage, 70-90 Kv, typically, less charge is available in the gun and as a result, the attraction between the paint or solid material sprayed by the spray gun toward the object to be painted tends to decline. The quality of the surface obtained thus decreases. In particular, there is an objectionable decline in the "wrap-around" effect. This effect, one of the most desirable aspects of electro-static spray coating, results in paint or solid material being deposited on the rear side of the object being painted.
There is thus an unfilled need for a diode-capacitor multiplier circuitry, which combines low energy storage with an acceptable surface being applied on the article being painted.